The field of devices with memory function is an important branch of semiconductor devices. Resistive random-access memory (RRAM) is an emerging non-volatile memory. The basic idea of RRAM is that a dielectric, which is normally not conductive, is made to conduct through a filament or conduction path formed after application of a voltage sufficiently high. The conduction path formation can arise from different mechanisms, including defects, metal migration, etc. Once the filament is formed, it may be reset (broken, resulting in high resistance) or set (re-formed, resulting in lower resistance) by an appropriately applied voltage. The advantage of RRAM is its simple structure and low processing cost.
There are many different RRAM solutions proposed, such as U.S. Pat. Nos. 6,531,371, 7,292,469, 6,867,996, 7,157,750, 7,067,865 and 6,946,702. Among them, a simple and cheap one is using native CuO formed at the interface of metal-1 Cu and the via between metal-1 Cu and metal-2 Cu as the dielectric. Thus RRAM can be made with the conventional dual-Damascene processing flow.
It has been found that the solution using CuO layer has many issues, including disturbance under small operation voltage and resistance distribution. These issues are mainly relative to the poor controllability of processing. There needs a new RRAM and manufacturing method, to improve the controllability of processing and the performance of devices.